Photo-electric cell



Feb. 10, 1931. KARQLUS ETAL 1,791,928

PHOTO ELECTRIC CELL Filed Jan. 5. 1927 INVENTOR AUGUST KAROLUS FR" SCHROETER a daw TIORNEY Patented Feb. 10, 1931 UNITED STATES PATENT OFFICE AUGUST KABOL'US,

or LEIPZIG, AND rnrrz scnno'rnn, or BERLIN, GERMANY, As

SIGNORS TO GESELLSCHAFT FUR DRAHTLOSE TELEGRAIPHIE M. B. H. HALLESCHES, 01E BERLIN, GERMANY, A CORPORATION OF GERMANY PHOTO-ELECTRIC CELL Application filed January 5, 1927, Serial No. 159,139, and in Germany January 8, 1926.

With reference to hotoelectric cells according to Elster and eitel and their use the suggestion has been made to work witlun a range inside which glow-discharge is al- 5 ready produced while yet the cell current decreases in the absence of inertia with the illumination which may be accomplished by raising the anode potential whereby the electrons generated by the light at the photoelectrically active electrode are drawn to the opposite electrode. If the highest possible cell currents are worked with bythis method, the limit is soon reached in the raising of the anode voltage by spontaneous glow-discharge which soon is initiated, and which continues even after darkening, and is not controllable by the light. I

According to our invention it is possible to substantially enlarge the working range of the preliminary glow-discharge which is still controllable by the light in an inertialess manner by the coaction of the following means so as to insure larger cell currents, to such an extent that currentsof over 1 milliamp. can still be supported by the cell without breaking down and can be quantitatively controlled by the light. A. necessary prerequisite is that, while the photoelectric emission surface is made of large area in well known manner, the anode potential 1s so adjusted that even with complete darkness, there is visible a feeble lumi nescence, with helium and neon filling clearly distinguishable, around the anode electrode or about its neighborhood. In other words, it is not a certain illumination which produces and leads up to this stage, but the same is present even in the presence of darkness, and is, of course, intensified with any increase in illumination of the photo-active surface.

As to the rest, this working range is characterized by confining luminescence to the region in the neighborhood of the anode electrode, and by the inability to distinguish, at

the time, a negative glow layer at the hotoelectric cathode. The change in con itions where the gl-owlayer is started is characterized by a steep rise in the cell current, and

m is therefore easily determinable.

In order to realize the said enlargement in the range of the utilizable cell currents, it has been found to be of substantial importance to provide as large an area as feasible for the anode electrode, compared with the geometrical extension of the electron-emitting electrode. The anode field is thus rendered rather homogeneous, the density of the positive charges in the vicinity of the anode electrode is diminished; hence, its influence upon the flattening of the current characteristic of the cell due to space-charge actions is diminished, and the danger of premature breakdown or starting of spontaneous glow-discharge on account of unduly large concentration of the positive carriers is prevented. In order that such a large-sized anode electrode may not become a hindrance to the free illumination of the photo-active layer issuing electrons, the former is given the shape of a network, grid or lattice, flat spiral of thin wires, or the like, in such a manner that the light is able to pass almost undiminished through the meshes or the interspaces of the anode electrode.

Another essential feature of the invention is that the gas filling consists of neon or helium, or mixtures thereof. These rare gases result in a particularlylarge working range of the cell, if a large surfaced anode electrode, as hereinbefore set forth, is employed. When neon is used as a filling, the value of the current attainable is over 1 inilliamp, as above pointed out. It is probable that the high anode tall of spontaneous discharge in these gases has a favorable action in the sense of afiording protection against all unstable conditions of the critical break down potential. Small additions of argon or hydrogen in neon or helium or their mixtures are of advantage, provided the total gas pressure remains at such a low figure that no influence of those admixtures tending to reduce the flashover voltage is noticeable.

The invention finally resides in the provision of additional electrical or magnetic fields to act upon the carrier paths or trajectories and the carrier impacts in the discharge space of the cell. The nature and purpose of these additional fields will be best understood by reference to Figs. 2 and 3.

The novel features which we believe to be characteristic of our invention are set forth in the appended claims, the invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following description read in connection with the accom panying drawings, wherein Fig. 1 is a cell, according to our invention, without an auxiliary field;

Fig. 2 is a cell similar to that of Fig. 1 with another electrode added; and,

Fig. 3 is a cell similar to Fig. 1 with a magnetic field introduced therein.

Referring now to Fig. 1 of the drawing, the cell is of flat lenticular shape and contains a photoelectrically active electrode K,

for instance hydride of potassium or another material of the series of metals or metallic alloys known to be active, as well as the anode .electrode S. The leads 1 and 2 of these two electrodes are arranged in the usual manner readily to be seen from the drawing. In conformity with the invention, the anode electrode is made in the form of a network, sieve, or grid-like construction and covers the entire extent of the opposite electrode K whereby the anode field is made more homogeneous and the advantages above outlined are obtained. It can be easily shown that if the electrode S is made smaller and smaller until, in the extreme case, it is punctiform, the working range of the cell is reduced, and breakdown is started at radually smaller currents, other conditions eing comparable or equal.

Making reference to Fig. 2 showing the addition of another electrode G formed similarly to the electrode S and having a lead 3, the said electrode G must be properly insulated both from S as well as from K. This can be easily attained by the convenient shaping of the stems or holders, and the provision'of long creepage distances or paths. If a positive potential is applied to S which is high compared with that applied to K, this potential acting across G can only influence partly the electrons released from K by the light (the amount of such action being governed by factors similar as in thermionic tubes and being known there as Durchgrifi meaning potential gradient or inverse amplification factor). The active acceleration potential can be very readily regulated by the potential of G, which, compared with K, may even be of negative value in certain cases. The result of the provision of the electrode G is that the electrons, after emerging from K are not accelerated to the same degree, so that in the space between the electrodes G and K they are unable to set up positive charges by collision, while attaining a very large energy growth between S and G, with the result that ionization in the neighborhood of S, or in other words, the desired preliminary glowdischarge (bias) is formed, and this in a readily regulable manner. On the other hand, withthe potential being conveniently adjusted, the positive carriers in the space between G and K can be retarded, so that the danger of premature breakdown of spontaneous glow-discharge can be controlled. By thus influencing the energy distribution and the collisions of the charges with the arrangement as hereinbefore described substantial advantages for the practical performance of the basic idea of the invention are derived.

Fig. 3 shows the use of a magnetic auxiliary field in which a magnetic pole M projects into the suitably shaped container. The magnetic pole may either form part of a permanent magnet, or of an electromagnet which is excited by means of turns of wire W Wound about the magnet. The magnetic force lines traverse the gas in the direction of the broken-line arrows, and as a result, the trajectories of the charges are curved, and the number of collisions increased, with the result that the cell current is able to rise considerably. Another point is that in this manner, to a certain extent, it is possible to regulate the energy with which the positive ions are made or allowed to impinge upon the electrode K, and it is this factor that governs the breakdown of the spontaneous glow-discharge. By allowing the production of an increased number of impacts by the positive ions in the gas, they are utilized as carriers in the assisted preliminary glow-discharge still controllable by light, while at the same time preventing them from liberating electrons by striking K to an extent which might be sufficient for the formation of the negative glow-discharge layer and thereby for the breakdown.

Photo-electric cells comprising auxiliary fields in the shape of charged grid electrodes are known. However, these are cells in which photo-electrically emitted electrons or predominantly electrons of this kind are not controlled, but rather in which electrons originating from an auxiliary electron source, for instance, an incandescent wire, are subject to primary control by the grid, (such as in cells with amplifier action, for example). Arrangements of this kind also serve other purposes than that of the present invention, for example, they have the object of avoiding inertia by the auxiliary electron source. In the present invention, on the other hand, the auxiliary fields by their influence upon the I energy distribution of the carriers, and the impacts in the discharge space, are intended to contribute to an enlargement of the use ful range of currents by raising the strength of the latter, and this is done without increasing the danger from. breakdown.

Other known cells as disclosed, for instance,in German Patent No. 282,708 comprising auxiliary grids, can not be regarded that controls the cell current, but rather a variable electric potential.

Having described our invention what we I claim is:

1. A photo cell comprising, an air tight envelope, a gas filling within said envelope, a

photoelectric member, and an anode member therein, and magnetic means for changing the trajectories of the electronic stream flowing between the photoelectric element and the anode for increasing the number of electronic impacts in said gas.

2. A photo cell comprising, an air tight envelope provided with an inset portion, a

gas filling within said envelope, a photo elec-- tric member, and an anode member therein, and magnetic means provided with a portion disposed in said inset portion of the envelope for changing the traj ectories of the electronic stream flowing between the photoelectric element and the anode for increasing the number of electronic impacts in said gas.

AUGUST KAROLUS. FRITZ sGHRoTER. 

